U.S. patent application number 12/418545 was filed with the patent office on 2010-06-17 for reworkable liquid crystal film and manufacturing method thereof.
This patent application is currently assigned to INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE. Invention is credited to Yih-Her CHANG, Ching-Yu CHEN, Jer-Young CHEN, Kung-Lung CHENG, Chih-Lung CHIN, Shih-Hsien LIU, Chang-Hung WU.
Application Number | 20100151228 12/418545 |
Document ID | / |
Family ID | 42240908 |
Filed Date | 2010-06-17 |
United States Patent
Application |
20100151228 |
Kind Code |
A1 |
CHIN; Chih-Lung ; et
al. |
June 17, 2010 |
REWORKABLE LIQUID CRYSTAL FILM AND MANUFACTURING METHOD THEREOF
Abstract
The invention provides a reworkable liquid crystal film,
including a first substrate, a first conductive layer disposed on
the first substrate, and a liquid crystal layer disposed on the
first conductive layer. The liquid crystal layer contains
microencapsulated liquid crystal droplets dispersed in a
thermoplastic polymer matrix. The invention also provides a method
for forming the reworkable liquid crystal film.
Inventors: |
CHIN; Chih-Lung; (Longtan
Township, TW) ; WU; Chang-Hung; (Guanyin Township,
TW) ; LIU; Shih-Hsien; (Jhubei City, TW) ;
CHENG; Kung-Lung; (Hsinchu, TW) ; CHANG; Yih-Her;
(Hsinchu City, TW) ; CHEN; Jer-Young; (Hsinchu
City, TW) ; CHEN; Ching-Yu; (Hsinchu City,
TW) |
Correspondence
Address: |
LOWE HAUPTMAN HAM & BERNER, LLP
1700 DIAGONAL ROAD, SUITE 300
ALEXANDRIA
VA
22314
US
|
Assignee: |
INDUSTRIAL TECHNOLOGY RESEARCH
INSTITUTE
Hsinchu
TW
|
Family ID: |
42240908 |
Appl. No.: |
12/418545 |
Filed: |
April 3, 2009 |
Current U.S.
Class: |
428/323 ; 156/60;
427/385.5; 428/336; 428/423.1; 428/480; 428/523 |
Current CPC
Class: |
B32B 27/08 20130101;
B32B 2307/412 20130101; B32B 27/36 20130101; B32B 2307/748
20130101; B32B 27/304 20130101; B32B 2264/0292 20130101; B32B
2457/202 20130101; B32B 27/283 20130101; B32B 27/32 20130101; B32B
2309/105 20130101; G02F 2202/28 20130101; B32B 2307/202 20130101;
B32B 2255/26 20130101; G02F 2203/68 20130101; Y10T 156/10 20150115;
Y10T 428/25 20150115; Y10T 428/31551 20150401; B32B 2307/718
20130101; B32B 27/281 20130101; B32B 27/308 20130101; B32B 2264/105
20130101; B32B 27/40 20130101; B32B 2264/0278 20130101; G02F 1/1334
20130101; B32B 2255/205 20130101; B32B 2367/00 20130101; B32B
2255/10 20130101; B32B 37/02 20130101; B32B 27/365 20130101; B32B
2037/243 20130101; B32B 2264/025 20130101; B32B 27/286 20130101;
Y10T 428/31938 20150401; Y10T 428/265 20150115; Y10T 428/31786
20150401; B32B 2250/40 20130101; B32B 2307/41 20130101; G02F
2202/022 20130101; B32B 27/306 20130101; B32B 2038/168
20130101 |
Class at
Publication: |
428/323 ;
428/423.1; 428/523; 428/480; 428/336; 427/385.5; 156/60 |
International
Class: |
B32B 5/16 20060101
B32B005/16; B32B 27/40 20060101 B32B027/40; B32B 27/30 20060101
B32B027/30; B32B 27/36 20060101 B32B027/36; B05D 3/00 20060101
B05D003/00; B32B 37/14 20060101 B32B037/14 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 15, 2008 |
TW |
097148718 |
Claims
1. A reworkable liquid crystal film, comprising a first substrate;
a first conductive layer disposed on the first substrate; and a
liquid crystal layer disposed on the first conductive layer,
wherein the liquid crystal layer comprises microencapsulated liquid
crystal droplets dispersed in a thermoplastic polymer.
2. The reworkable liquid crystal film as claimed in claim 1,
wherein the thermoplastic polymer comprises polyvinyl alcohol
(PVA), polyurethane (PU), polyacrylic acid (PAA), polyvinyl
pyrrolidone (PVP), polyvinyl acetate (PVAc), or combinations
thereof.
3. The reworkable liquid crystal film as claimed in claim 1,
wherein the thermoplastic polymer has an ion content of less than
100 ppm.
4. The reworkable liquid crystal film as claimed in claim 1,
wherein the thermoplastic polymer has an ion content of less than
1000 ppm.
5. The reworkable liquid crystal film as claimed in claim 1,
wherein the thermoplastic polymer has a weight-average molecular
weight of about 27000-32000.
6. The reworkable liquid crystal film as claimed in claim 1,
wherein the thermoplastic polymer has an average degree of
polymerization of about 550-650.
7. The reworkable liquid crystal film as claimed in claim 1,
wherein the liquid crystal layer has a thickness of about 10-20
.mu.m.
8. The reworkable liquid crystal film as claimed in claim 1,
further comprising a second conductive layer disposed on the liquid
crystal layer, and a second substrate disposed on the second
conductive layer.
9. The reworkable liquid crystal film as claimed in claim 1,
further comprising a release film disposed on the liquid crystal
layer.
10. The reworkable liquid crystal film as claimed in claim 1,
wherein the microencapsulated liquid crystal droplets have a
particle size of about 1-6 .mu.m.
11. The reworkable liquid crystal film as claimed in claim 1,
wherein the first substrate is disposed on a curved surface.
12. A method for forming a reworkable liquid crystal film,
comprising mixing microencapsulated liquid crystal droplets with an
adhesive to provide a liquid crystal coating material, wherein the
adhesive is an aqueous solution of a thermoplastic polymer; coating
the liquid crystal coating material onto a substrate with a
conductive layer thereon; and drying the liquid crystal coating
material to form a dried film.
13. The method for forming a reworkable liquid crystal film as
claimed in claim 12, wherein the aqueous solution has a
concentration of about 5-35%.
14. The method for forming a reworkable liquid crystal film as
claimed in claim 12, wherein the aqueous solution has a
concentration of about 10-30%.
15. The method for forming a reworkable liquid crystal film as
claimed in claim 12, wherein the liquid crystal coating material
has a solid content of about 20-60%.
16. The method for forming a reworkable liquid crystal film as
claimed in claim 12, wherein the thermoplastic polymer comprises
polyvinyl alcohol (PVA), polyurethane (PU), polyacrylic acid (PAA),
polyvinyl pyrrolidone (PVP), polyvinyl acetate (PVAc), or
combinations thereof.
17. The method for forming a reworkable liquid crystal film as
claimed in claim 12, wherein the thermoplastic polymer has an ion
content of less than 1000 ppm.
18. The method for forming a reworkable liquid crystal film as
claimed in claim 12, wherein the thermoplastic polymer has an ion
content of less than 100 ppm.
19. The method for forming a reworkable liquid crystal film as
claimed in claim 12, wherein the liquid crystal coating material is
dried at a temperature of about 40-90.degree. C.
20. The method for forming a reworkable liquid crystal film as
claimed in claim 12, further comprising laminating the dried film
with another substrate with a conductive layer thereon.
21. The method for forming a reworkable liquid crystal film as
claimed in claim 12, further comprising laminating the dried film
with a release film.
22. The method for forming a reworkable liquid crystal film as
claimed in claim 12, which is implemented on a continuous,
roll-to-roll process.
23. The method for forming a reworkable liquid crystal film as
claimed in claim 12, further comprising attaching the liquid
crystal film onto a curved surface.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of Taiwan Patent
Application No. 097148718, filed on Dec. 15, 2008, the entirety of
which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a liquid crystal film, and
in particular relates to a reworkable, electrically switchable
liquid crystal film.
[0004] 2. Description of the Related Art
[0005] Smart glass, or so-called switchable window, refers to an
electrically switchable glass which changes light transmission
properties when voltage is applied. A thin layer of liquid crystals
is sandwiched between two layers of glass or plastic that include a
layer of a transparent, conductive material as electrodes. With no
applied voltage, the liquid crystals are randomly arranged,
resulting in scattering of light as it passes through the liquid
crystal layer. This results in a translucent, "milky white"
appearance. When a voltage is applied to the electrodes, the
electric field formed between the two transparent electrodes on the
glass causes the liquid crystals to align, thereby allowing light
to pass through with very little scattering, resulting in a
transparent state. The degree of transparency can be controlled by
the applied voltage. Smart glass is applied in aircrafts,
automobiles, architectural glass, outdoor advertising modules,
bathrooms, conference rooms, and video walls.
[0006] The liquid crystal used in conventional smart glass is a
polymer dispersed liquid crystal (PDLC) film, wherein the liquid
crystals are dissolved or dispersed into a liquid polymer followed
by solidification or curing of the polymer. During curing of the
polymer, the liquid crystals become incompatible with the solid
polymer and form droplets throughout the solid polymer. However,
the PDLC film tends to have obvious light leakage when pressed or
bent, which make it undesirable for curved-surface applications
such as car windshields. This phenomena could be attributed to the
non-uniformity in size of liquid crystal droplets formed by the
curing process. Furthermore, the PDLC film cannot be fabricated by
a continuous roll-to-roll process, and is not detachable, i.e., not
reworkable.
[0007] Accordingly, it would be desirable to provide a reworkable,
electrically switchable liquid crystal film which can be fabricated
by a continuous roll-to-roll process and has reduced or no light
leakage when pressed or bent.
BRIEF SUMMARY OF THE INVENTION
[0008] The invention provides a reworkable liquid crystal film,
comprising: a first substrate; a first conductive layer disposed on
the first substrate; and a liquid crystal layer disposed on the
first conductive layer, wherein the liquid crystal layer comprises
microencapsulated liquid crystal droplets dispersed in a
thermoplastic polymer.
[0009] The invention also provides a method for forming a
reworkable liquid crystal film, comprising: mixing
microencapsulated liquid crystal droplets with an adhesive to
provide a liquid crystal coating material, wherein the adhesive is
an aqueous solution of a thermoplastic polymer; coating the liquid
crystal coating material onto a substrate with a conductive layer
thereon; and drying the liquid crystal coating material to form a
dried film.
[0010] A detailed description is given in the following embodiments
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The present invention can be more fully understood by
reading the subsequent detailed description and examples with
references made to the accompanying drawings, wherein:
[0012] FIG. 1 is a flow chart showing the method for forming a
liquid crystal film according to an embodiment of the
invention;
[0013] FIG. 2 is a schematic view showing an apparatus for forming
the liquid crystal film of the invention by a continuous
roll-to-roll process;
[0014] FIG. 3 is a cross-sectional view of the liquid crystal film
according to an embodiment of the invention;
[0015] FIG. 4 is a cross-sectional view of the liquid crystal film
according to another embodiment of the invention;
[0016] FIGS. 5-9 are transmission-versus-voltage curves for the
liquid crystal films of Examples 1-2 and a commercial product;
and
[0017] FIG. 10 shows transmission-versus-voltage curves for the
liquid crystal films of Example 7.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The following description is of the best-contemplated mode
of carrying out the invention. This description is made for the
purpose of illustrating the general principles of the invention and
should not be taken in a limiting sense. The scope of the invention
is best determined by reference to the appended claims.
[0019] The invention involves mixing microencapsulated liquid
crystal droplets with thermoplastic polymer adhesive to provide a
liquid crystal coating material. The electrically switchable liquid
crystal film of the invention can be delaminated/relaminated and
has reduced or no light leakage when pressed or bent, thereby
providing a higher degree of concealment. Furthermore, the
fabrication processes may be implemented by a large scale area
roll-to-roll production line.
[0020] The invention is described in more detail by referring to
the flow chart of FIG. 1, which shows the method for forming a
liquid crystal film according to an embodiment of the invention.
The method begins by mixing microencapsulated liquid crystal
droplets with thermoplastic polymer adhesive to provide a liquid
crystal coating material (step S100). For the conventional polymer
dispersed liquid crystal (PDLC), the liquid crystal material is
directly dispersed in polymeric resin. On the other hand, for the
polymer dispersed microencapsulated liquid crystal (PDMLC) used in
the invention, the liquid crystal material is microencapsulated by
a capsule wall to form liquid crystal microcapsules dispersed in
polymeric resin. The liquid crystal material to be
microencapsulated may be either nematic, cholesteric, smectic, or
ferroelectric. The capsule wall may be composed of polyurethane,
polyurea, polyacrylate, polyacrylic acid, epoxy resin, polyester,
or their combinations. Information relevant to microencapsulated
liquid crystals and fabrication methods thereof can be found in
U.S. Pat. No. 6,120,701, the entirety of which is incorporated by
reference herein. The size of the microencapsulated liquid crystal
droplets is about 1-6 .mu.m. A slurry containing the synthesized
liquid crystal microcapsules can be centrifuged to obtain narrow
particle size distribution, which is an important advantage
afforded by the microencapsulated liquid crystals.
[0021] The polymeric adhesive used herein is an aqueous solution of
a thermoplastic polymer, which preferably has a concentration of
about 5-35%, more preferably about 10-30% (by weight). Suitable
thermoplastic polymers include, but are not limited to, polyvinyl
alcohol (PVA), polyurethane (PU), polyacrylic acid (PAA), polyvinyl
pyrrolidone (PVP), polyvinyl acetate (PVAc), or combinations
thereof, wherein polyvinyl alcohol (PVA) is particularly preferred.
In one example, a thermoplastic polymer with a weight-average
molecular weight of about 27000-32000, and an average degree of
polymerization of about 550-650 is used. According to a feature of
the invention, a thermoplastic polymer of low ion content is
preferably used as an adhesive. For example, the level of ion
content is preferably lower than 100 ppm, more preferably lower
than 1000 ppm. The use of a low ion content thermoplastic polymer
can reduce leakage current, thus improving the performance of the
electrically switchable liquid crystal film.
[0022] In one embodiment, microencapsulated liquid crystal and
thermoplastic polymer adhesive are uniformly mixed at a weight
ratio of about 1:1-3 at room temperature. The liquid crystal
coating material thus formed may have a solid content of about
20-60%, preferably about 30-50%, and a viscosity at 25.degree. C.
of about 800-2000 cps, preferably about 1000-1200 cps.
[0023] Thereafter, the liquid crystal coating material containing
the microencapsulated liquid crystal droplets and thermoplastic
polymer adhesive is coated on a substrate having a conductive layer
thereon, for example, an indium tin oxide coated polyester
(ITO-PET) film (step S110). The coated liquid crystal material is
then dried into a liquid crystal film (step S120), and then
laminated with another substrate having a conductive layer thereon
to provide the electrically switchable liquid crystal film of the
invention (step S130).
[0024] The fabrication steps S110, S120, S130 are preferably
carried out by a roll-to-roll process to provide a continuous
liquid crystal film roll. FIG. 2 is an example of a roll-to-roll
apparatus for fabricating the liquid crystal film. As shown in FIG.
2, an ITO-PET film 15 is unwound by a dispenser roller 30 and
continuously carried at a fixed speed of, for example, about 2-4
m/min. Through a slot die 40, the liquid crystal coating material
20 obtained from step S100 is coated onto the ITO-PET film 15 at
roller 10. The coated film is subsequently dried when passing
through a drying oven 60. The coated film may be dried in the oven
by a multi-stage drying process with temperatures ranging from
about 40-90.degree. C. Thereafter, the dried coating film is
laminated with another ITO-PET film 25 by a heat roller 80 to give
the desired electrically switchable liquid crystal film 35, which
is then rolled onto a take-up roller 50. It should be noted that
FIG. 2 merely shows a representative roll-to-roll apparatus for
practicing the invention. Apparatuses other than that shown in FIG.
2 can be used to practice the invention.
[0025] FIG. 3 is a cross-sectional view of the liquid crystal film
according to an embodiment of the invention. As shown, the
electrically switchable liquid crystal film includes a first
substrate 100, a first conductive layer 150 disposed on the first
substrate 100, and a liquid crystal layer 300 disposed on the first
conductive layer 150. The liquid crystal layer 300 contains a
plurality of microencapsulated liquid crystal droplets 320
dispersed in a thermoplastic polymer 310, wherein the
microencapsulated liquid crystal droplets 320 are composed of a
capsule wall 320b and the liquid crystal molecules 320a enclosed in
the capsule. The microencapsulated liquid crystal droplets 320 and
the thermoplastic polymer 310 in the liquid crystal layer 300 are
preferably present at a weight ratio of about 1:2, and more
preferably about 1:1.5. Above the liquid crystal layer film, there
is further provided a second conductive layer 250 and a second
substrate 200. The first and second conductive layers 150, 250
serve as electrodes that control the alignment direction of the
liquid crystal molecules 320a. When no voltage is applied, the
liquid crystal molecules 320a are randomly arranged in the droplets
320, resulting in scattering of light as it passes through the
liquid crystal layer film 300. As a result, the electrically
switchable liquid crystal film is opaque or translucent. When
voltage is applied to the electrodes, the liquid crystal molecules
320a align parallel to the applied field, thereby allowing light to
pass through the droplets 320 with very little scattering, and the
electrically switchable liquid crystal film becomes clear and
transparent.
[0026] The first and second conductive layers 150, 250 are
transparent conductive layers such as indium tin oxide (ITO),
indium zinc oxide (IZO), and aluminum-doped zinc oxide (AZO). The
first and second substrates 100, 200 can be any transparent
polymers such as polycarbonate (PC), poly(ethylene 2,6-naphthalate)
(PEN), polyimide (PI), and poly(ether sulfone) (PES). Additionally,
if a continuous roll-to-roll process is not applied, rigid
transparent substrates such as glass may be used. The thickness of
the liquid crystal layer 300 may range from about 10 .mu.m to about
20 t.mu.to cope with the demand of high transparency (thin film) or
high shielding (thick film). The thickness may be adjusted by
controlling the viscosity of the coating material, the width of the
slot die, the feeding speed of the substrate, and so on.
[0027] One advantage of the electrically switchable liquid crystal
film of the invention is that it exhibits a remarkably reduced
light leakage when being pressed or bent. This result is attributed
to the narrow size distribution of the microencapsulated liquid
crystal droplets and the fact that the liquid crystals enclosed in
the capsule are less flowable or deformable due to external forces.
This feature allows the electrically switchable liquid crystal film
to be used on a curved surface such as car windshields,
architectural glass, or other shaped glass with a non-planar
surface. By contrast, conventional electrically switchable liquid
crystal films may substantially lose the switchable characteristic
due to significant light leakage when applied to curved
surfaces.
[0028] Another advantage of the electrically switchable liquid
crystal film of the invention is the reworkable property; that is,
it can be delaminated and reprocessed. Because the adhesive used
herein is a thermoplastic polymer, the second substrate 200
(including the second conductive layer 250 thereon) laminated on
the liquid crystal layer 300 is readily detachable and can be
relaminated without adversely affecting the electro-optical
performance. By contrast, conventional electrically switchable
liquid crystal films that use thermoset polymer adhesives such as
epoxy resins, are not detachable once laminated on a substrate,
thus they are not suited for rework or further processing.
[0029] Referring to FIG. 4, a cross-sectional view of the liquid
crystal film according to another embodiment of the invention is
shown. In this embodiment, the second substrate 200 and the second
conductive layer 250 of FIG. 3 that overly the liquid crystal layer
300 are replaced by a release film 400. The release film can be
made of PET, polypropylene (PP), polyethylene (PE), polyvinyl
chloride (PVC), or silicone. The release film preferably has a
thickness of about 10-100 .mu.m. A liquid crystal film with a
release film attached thereto can be fabricated simply by replacing
the ITO-PET film 25 of FIG. 2 with a release film. The product
containing the release film can be cut into a suitable size after
the size of a demanded smart window is determined. After cutting,
the release film 400 can be removed from the surface of the liquid
crystal layer 300, and then an ITO-PET film or other conductive
substrates (such as ITO-glass substrate) of a predetermined size
can be laminated, thus providing process adjustability.
SYNTHETIC EXAMPLE
[0030] 2.5g of polyurethane (Desmodur N-3200 manufactured by Bayer
Corp.) and 40 g of liquid crystal (DII-032 manufactured by the
Industrial Technology Research Institute, Taiwan, .DELTA.n=0.19,
Tc=89.degree. C.) were mixed at 60.degree. C. The solution was then
poured into a solution of 200 g of 10% polyvinyl alcohol, which was
undergoing constant stirring, and was emulsified at 3000 rpm, 50 to
55.degree. C. for 3 minutes to obtain the particle size of 1 to 10
.mu.m. 25 g of 10% triethylene diamine and 25 g of 10% triethanol
amine were added to the solution and stirred at 55.degree. C. for
10 hours. After the reaction was complete, 20 g of 10% ammonium
hydroxide was added to the solution and then the solution was
allowed to stand overnight. The resulting slurry was centrifuged at
5000 rpm to obtain a microencapsulated liquid crystal of narrow
particle size distribution of 1 to 5 .mu.m.
EXAMPLE 1
[0031] At room temperature, the microencapsulated liquid crystal of
the Synthetic Example was mixed with an aqueous solution of 20%
polyvinyl alcohol at a weight ratio of 1:1.5 to obtain a liquid
crystal coating material having a solid content of 42%, and a
viscosity of 1000-1100 cps (at 25.degree. C.). For the mixed
aqueous solution, the polyvinyl alcohol weight-average molecular
weight was 27000-32000, the average degree of polymerization was
550-650, and the sodium ion content was below 60ppm.
[0032] Using the apparatus as shown in FIG. 2, the liquid crystal
coating material was coated on an ITO-PET film by a slot die
(coating width: 1.1 m) at a line speed of 4 m/min, dried in an oven
by a five-stage drying process with temperatures ranging from 40 to
90.degree. C., and then laminated with another ITO-PET film by heat
rollers at about 100.degree. C., thus obtaining an electrically
switchable liquid crystal film with a thickness of 15 .mu.m.
EXAMPLE 2
[0033] The same procedure as described in Example 1 was repeated to
obtain an electrically switchable liquid crystal film, except that
the liquid crystal coating material was prepared by mixing the
microencapsulated liquid crystal with a 20% polyvinyl alcohol
aqueous solution and a 20% polyurethane aqueous solution at a
weight ratio of 1:1.29:0.21. The resulting coating material had a
solid content of 42% and a viscosity of 800-900 cps (at 25.degree.
C.).
EXAMPLE 3
[0034] Each of the electrically switchable liquid crystal films of
Examples 1-2 was cut into a suitable size and bonded with two glass
sheets on opposite sides to obtain an electrically switchable glass
(size: 1.1 m.times.3 m). The opto-electrical characteristic of the
electrically switchable glass was measured by a transparency meter
(manufactured by EDTM Inc.), and the results are shown in FIG. 5.
As can be seen, the electrically switchable liquid crystal film of
Example 1 exhibited a higher transmission (T %=65% at 45V) than the
commercial product "Polyvision.TM." (T %=54% at 45V, available from
Polytronix, Inc.).
EXAMPLE 4
[0035] The same procedure as described in Example 1 was repeated
except that the distance between the slot die and the ITO-PET
substrate was changed to prepare electrically switchable liquid
crystal films of different thicknesses (dry film thickness: 10
.mu.m and 17 .mu.m, not including the substrate thickness). Each of
the electrically switchable liquid crystal films was cut into a
suitable size and bonded with two glass sheets on opposite sides to
obtain an electrically switchable glass. The opto-electrical
characteristic was measured and the results are shown in FIG. 6 and
the following table.
TABLE-US-00001 Transmission (%) Applied voltage Thickness: 17 .mu.m
Thickness: 10 .mu.m 0 V 7 10 50 V 66 70
[0036] As can be seen, the thick film (17 .mu.m) showed a
relatively poor transmission (7%-66%) or higher shielding, while
the thin film (10 .mu.m) showed a relatively higher transmission
(10%-70%) or poor shielding.
EXAMPLE 5
[0037] The ITO-PET substrate of the electrically switchable liquid
crystal film of Example 1 was delaminated and relaminated for three
times, wherein the relamination was carried out by a laminator at
100.degree. C. The relaminated sample was measured for the
opto-electrical characteristic. As shown in FIG. 7, the
opto-electrical characteristic was almost unchanged as compared to
the original sample.
EXAMPLE 6
[0038] A commercial smart glass product "Polyvision.TM." from
Polytronix, Inc. (21 cm.times.8 cm in size) was bent into a hollow
cylindrical shape (6cm in diameter), and measured for the
opto-electrical characteristic. As shown in FIG. 9, when no voltage
was applied, the commercial product showed a transmission of 3%
before bending. However, the transmission was significantly
increased by 12%, to 15% after bending.
[0039] Likewise, the electrically switchable liquid crystal film of
Example 1 of the same size (21 cm.times.8 cm) was bent into a
hollow cylindrical shape (6 cm in diameter), and measured for the
opto-electrical characteristic. As shown in FIG. 9, when no voltage
was applied, the transmission was 6% before bending, and slightly
increased by 1%, to 7% after bending. This unique features allows
the electrically switchable liquid crystal film of the invention to
be applied on a curved surface without substantial light leakage to
maintain a high degree of concealment.
EXAMPLE 7
[0040] The same procedure as described in Example 1 was repeated to
obtain the liquid crystal coating material, except that 20%
polyvinyl alcohol aqueous solutions with a low ion content (below
60 ppm) and a high ion content (above 3600 ppm) were used,
respectively. Each of the obtained liquid crystal coating material
was coated on an ITO-PET film by blade coating, oven dried at about
80-90.degree. C. for 7 minutes, and then laminated with another
ITO-PET film by a laminator at about 100.degree. C., thus obtaining
an electrically switchable liquid crystal film with a thickness of
8 .mu.m and 15 .mu.m, respectively.
EXAMPLE 8
[0041] Each of the electrically switchable liquid crystal films of
Example 7 was cut into a suitable size and bonded with two glass
sheets on opposite sides to obtain an electrically switchable glass
(size: 1.1 m.times.3 m). The opto-electrical characteristic of the
electrically switchable glass was measured by a transparency meter
(manufactured by EDTM Inc.), and the results are shown in FIG. 10.
As can be seen, the electrically switchable liquid crystal film
(thickness: 8 .mu.m and 15 .mu.m) made from the low-ion-content PVA
solution exhibited a higher transmission than that made from the
high-ion-content PVA solution. Furthermore, with a thickness above
15 .mu.m, the electrically switchable liquid crystal film made from
the high-ion-content PVA solution was burnt out and substantially
lost the switchable function after several times of voltage
application.
[0042] While the invention has been described by way of example and
in terms of the preferred embodiments, it is to be understood that
the invention is not limited to the disclosed embodiments. To the
contrary, it is intended to cover various modifications and similar
arrangements (as would be apparent to those skilled in the art).
Therefore, the scope of the appended claims should be accorded the
broadest interpretation so as to encompass all such modifications
and similar arrangements.
* * * * *